Coating aluminium oxide ceramics with hydroxyl apatite

ABSTRACT

The invention relates to a method for producing hydroxyapatite coated ceramics components. In a first step of the inventive method the ceramic component is provided with a Ti coating and in a second step a hydroxyapatite is applied to the Ti coating. The invention further relates to hydroxyapatite coated ceramic components produced according to the inventive method.

[0001] The subject of the present invention is a method for themanufacture of ceramic components coated with hydroxyapatite, as well asthe ceramic components which can be manufactured by this method.

[0002] It is known that prostheses which have a hydroxyapatite coatingdisplay an especially good ingrowth activity. Care must be taken,however, to see that the hydroxyapatite coating firmly adheres to theprosthesis. In the coating of titanium shafts with hydroxyapatite anespecially great strength of adherence can be achieved when the metalsurface is given a roughness of R_(a)≈40-50 μm.

[0003] The adhesive strength of hydroxyapatite apatite on ceramicsurfaces, especially on Al₂O₃ ceramics, is not sufficient for thedesired use. Thus any direct coating of an aluminum oxide ceramic withhydroxyapatite, such as would be very advantageous for the directfixation of the femur part of a knee prosthesis, is impossible. Even ifthe surface roughness is made similar to the roughness of the titaniumshafts, the strength of the adhesion of hydroxyapatite is not assured.This has been proven in experiments in which ground and sand-blastedsamples were used. In comparison with titanium materials the surfaceroughness of ceramic base materials thus treated is substantially lower.Coating tests with the standard parameters for titanium shafts resultedin no strength of adhesion between hydroxyapatite and aluminum oxideceramic. Inasmuch as no coating adhered to aluminum oxide bodies understandard conditions, the spray parameters was also modified in theplasma coating apparatus. But even the modified process parameters didnot lead to success. The cause of the poor strength of adhesion wasdetermined to be the differences in roughness between the metal and theceramic. A surface roughness of R_(a)≈30 μm cannot be achieved byconventional abrasive methods.

[0004] Even methods which lead to increased depth of roughness did notbring the desired success. To produce a greater defined surfaceroughness, similar specimens were prepared for laser machining undervarious settings. In this manner it was possible to produce a lastingeffect on the surfaces of the Al₂O₃ ceramic. While in the case of normalgrinding a raw depth of no more than 1 μm could be achieved, the lasertreatment succeeded in producing a raw depth of R_(a)≈9 μm. FIG. 3 showsthe typical surface after the laser treatment. The lasered surface ofthe aluminum oxide ceramic was then subjected to plasma coating withhydroxyapatite. For the first time a few placed on this surface weredetected, on which the hydroxyapatite coating could be detected. Ofcourse, it was not possible even by this preliminary treatment to applya continuous coating. FIGS. 4 and 5 show the surfaces of the lasered andhydroxyapatite (HA) coated specimens.

[0005] Even though it was possible for the first time to prove thedeposition of hydroxyapatite on the roughened surfaces of the aluminumoxide ceramic, the strength of adhesion of the coating was very poor.Quantification of the strength of adhesion was impossible, as was thepreparation of a transverse section; the coating fell off immediately.Again, when the raw depth was analyzed it was compared with that ofmetal materials. With an R_(a) of 9 μm the raw depth of the TiAl6V4-1alloy (R_(a)≈40 μm) could not be achieved. It was necessary to refrainfrom any further roughening of the surface in the ceramic substrate,since the aluminum oxide ceramic, unless metallic materials, has anabsolute cleavage fracture tendency. If a “predamage” of 40 μm isinduced, this “flaw” can trigger breakage. Thus, any further increase ofthe roughness is impossible from the viewpoint of fracture mechanics.

[0006] The present invention is addressed to the problem of makingavailable a method by which ceramic components can reliably be providedwith a hydroxyapatite coating.

[0007] The problem to which the invention is addressed has been solvedby a method with the features of the principal claim. Preferredembodiments are described in the subclaims.

[0008] Surprisingly it was possible according to the invention to coat aceramic component, preferably a component made of aluminum oxideceramic, with hydroxyapatite if the surface of the ceramic component iscoated with a titanium layer. By the method of the invention it issurprisingly possible for the first time to deposit hydroapatic on thesurface of a ceramic component, with sufficient strength of adhesion.

[0009] According to the invention, first ceramic components are providedwith a thin titanium coating, for example by PVD (physical vapordeposition). According to the invention, the surface of the ceramiccomponent can be previously roughened,—ground or lasered, for example.The thickness of the titanium layer was about 1 μm; a coating 5 μm thickalso led to success. FIG. 6 shows the transverse section of a specimencoated in this manner.

[0010] The hydroxyapatite layer was sprayed onto this intermediatelayer. The transverse section of this built-up coating is represented inFIGS. 7 and 8 at different enlargements.

[0011] Preferably, before the hydroxyapatite is applied by plasmacoating, for example, the titanium intermediate layer is subjected alsoto a sand blasting process to improve adhesion. An especially highstrength of adhesion is achieved if the titanium coating is given aroughness of R_(a)≈40-50 μm.

[0012] A scratch test on the hydroxyapatite coating confirmed theoutstanding strength of adhesion of the coating. Preparation of atransverse section was possible without problems. The measurement of thestrength of adhesion was made on five different specimens. Theindividual values are summarized in Table 1. TABLE 1 Strength ofadhesion of hydroxyapatite on Al₂O₃ with titanium primer Specimen Force[N] Tension [MPa] 1 718 2.3 2 1203 3.8 3 932 3 4 1490 4.7 5 390 1.2

[0013] From the values obtained by the strength-of-adhesion measurementsit can be seen that tensions are surprisingly achieved which are in therange of that of hydroxyapatite coatings on TiAl6V4 alloys.

[0014] According to the invention, it is also possible, instead of theconventional titanium intermediate coating, an intermediate coating ofthe TiAl6V4 alloy can be deposited, for example by the PVD method.

[0015]FIG. 9 shows the typical building of layers in the preparation oftransverse sections. The corresponding strengths of adhesion are listedin Table 2. Specimen Force [N] Tension [MPa] 1 582 1.9 2 700 2.2 3 4001.3 4 498 1.6

[0016] A ceramic component in the form of a cylindrical test specimenwas used in the tests. The cylinders, with a diameter of 20 mm and athickness of 2 mm, were made he conventional press-turn manufacture asgreenbodies, subjected to hot isostatic pressure and annealed. Thesintered bodies were then machined with diamond tools to achieve finalshape. Other methods for the manufacture of ceramic components can, ofcourse, also be used. Used as the material was a known aluminum oxidematerial, such as the one known as Biolox® material, for example.

[0017] With the present invention it is thus for the first time possibleby providing a titanium intermediate coating to deposit hydroxyapatitedirectly onto ceramic components. The ceramic components that can bemade by the method of the invention are also subject matter of thepresent invention.

[0018] Thus, according to the invention, ceramic components can for thefirst time be made, which can be used for medical purposes, for exampleas prostheses. Such prostheses display an improved ingrowthcharacteristic.

1. Method for the manufacture of hydroxyapatite coated ceramiccomponents, characterized in that in a first step the ceramic componentis first provided with a Ti coating and in a second step thehydroxyapatite is applied to the Ti coating.
 2. Method according toclaim 1, characterized in that the surface of the ceramic component isroughened before the first step.
 3. method according to claim 1 or 2,characterized in that the Ti coating applied in the first step is rough.4. Method according to one or more of claims 1 to 3, characterized inthat the Ti coating applied in the first step is adjusted to a roughnessof R_(a)≈40 to 50 μm.
 5. Method according to one or more of claims 1 to4, characterized in that in the first step the titanium is depositedonto the surface of the ceramic component by means of the PVD process.6. Method according to one or more of claims 1 to 5 characterized inthat, instead of the Ti coating, by means of the PVD process a coatingof the TiAl6V4 alloy is deposited.
 7. Method according to one or more ofclaims 1 to 6, characterized in that the Ti or TiAl6V4 coating appliedin the first step is 5 μm thick.
 8. Method according to one or more ofclaims 1 to 7, characterized in that the Ti or TiAl6V4 layer applied inthe first step is between 1 and 5 μm thick.
 9. Method according to oneor more of claims 1 to 8, characterized in that the hydroxyapatite issprayed onto the Ti or TiAl6V4 coating applied in the first step. 10.Method according to one or more of claims 1 to 9, characterized in thatthe hydroxyapatite is applied to the Ti or TiAl6V4 coating by plasmacoating.
 11. Method according to one or more of claims 1 to 10,characterized in that the ceramic component is an aluminum oxideceramic.
 12. Method according to one or more of claims 1 to 11,characterized in that the ceramic component is a medical component. 13.Method according to one or more of claims 1 to 11, characterized in thatthe ceramic component is a prosthesis.
 14. Hydroxyapatite coated ceramiccomponent manufacturable according to one or more of the foregoingclaims.